I wonderif it's possible - - -
to have that speech be MLK's personal property AND have the use of it in the public domain? In other words by broadcasting it over nationwide TV, by not protesting it's unrestricted use while he was alive, that he forfeited the right to limit reproduction.
What gives it value is the widespread attribution. To then attempt to limit it's distribution is not only counter to King's wishes while he was alive but to sandbag those who in good faith have quoted it. I think the use of it has passed into the public domain by usage.